This invention relates to superfine fibers with a high ion-exchange capacity, obtained from a polyvinyl alcohol type fiber (hereinafter referred to as PVA fiber).
Since an ion-exchange reaction relies on a contact reaction between radicals of an ion-exchanger and substrates to be ion-exchanged, the more chances of both contacting, the higher a reaction rate. Therefore the larger a surface area of ion-exchangers and the more radicals present on the surface, the faster an ion-exchange reaction. Ion-exchange resins in the form of particles are in general used as materials having an ion-exchange capacity. The particulate ion-exchange resins, however, have a disadvantage that the ion-exchange velocity is low because of a small surface area.
For overcoming the disadvantage porous resins were provided, but the effects of having increased the surface area were not substantially attained in that openings of the porous resin are blocked and reaction products are not conveniently recycled in the openings. Fine powders obtained by pulverization of particulate resins had some effects, though the handling was difficult because of a particle size being too small.
For overcoming such disadvantages processes for the preparation of ion-exchange fibers were disclosed, for example, in Japanese Patent Publication No. 51-44712, Japanese Patent Application Kokai Nos. 51-38526 and 53-4787. These ion-exchange fibers exhibit good properties having 10-20 times the exchange velocity as compared with the conventional ion-exchange resins. On the other hand, fibers obtained by conventional spinning conditions have a diameter of 10-30.mu. and making the fiber diameter smaller is desired for increasing the fiber surface area. However, with conventional spinning methods about 10.mu. in diameter is the lower limit and spinning fibers of smaller diameter is very difficult from the points of filament's breaking and its handling.